You have created a nice, well written function, but you realize you forgot something: The failure case. What should a function do when it fails? There are two schools for this - the “throw an exception” school and the “return an error value” school. But which of these is the correct approach?

He suggests that this debate has stuck around from the time when there weren't exceptions in several popular programming languages and that returning the value was the only valid way. He touches on what an exception condition is (with a few code examples) and situations where each choice might be the right way to go.